What Are They?
Grids are an imaginary set of vertical and horizontal lines that go over your layout.
Grids are the civil engineers of the design world. They keep information organized, straight and easy to navigate. They guide the eye through the design and allow the information to flow logically. Grids are like the moving sidewalks at an amusement park. They just keep things moving in an organized fashion.
Setting One Up
It starts with the layout boundary. Draw margins around your layout. Then add column guides to create the vertical grids. Then add horizontal lines as needed to make a more complex grid.
Don't be afraid to break the grid. Although they are easy and navigable, they can be boring and routine. Bleed an image off the page or rotate something to break up the rigidness and make the design more fluid.